The present invention relates generally to prefabricated buildings and more particularly to improved prefabricated panels and related assembly techniques.
Prefabricated construction owes its success to the economies of mass production and minimization of field assembly labor and skill. Accordingly, attention has focused in the art on simplification of both manufacturing and field assembly techniques using modular panels which may be arranged in abutting relationship to form the walls and roof of a building. Typical prior art panels comprise thin metal sheets having strengthening corrugations and an insulating core of foam formed in place between the sheets.
One such prior art system is described in U.S. Pat. No. 3,290,845. The opposite edges of the panel described therein are adapted to mate with adjacent edges of similarly constructed panels. In particular, overlapping members are formed by extensions of the thin exterior material beyond the insulating layer at one panel edge to overlap a portion of the opposite edge of an adjacent panel. Pop rivets are used to secure the overlapping extension to the underlying member. The use of pop rivets as fasteners is relatively economical for assembly purposes; however, they present problems in the event panels need to be disassembled for any of various reasons. It would be desirable, therefore, to employ a fastening technique which permits disassembly of panels with relative ease, without damage to the panels and without sacrificing economy.
The use of "self-drilling" screws would achieve the desired purpose of convenient, non-damaging disassembly. Additionally, such threaded fasteners would save labor during initial installation when compared to pop rivets. A pop rivet requires the two separate operations of drilling a hole at the desired location and then installing the pop rivet therein. On the other hand, a self-drilling screw forms its own hole while being installed, as not surprisingly the name itself implies. Unfortunately, however, the relatively thin sheet metal faces of the metal-foam-metal prefabricated panels of the prior art are not sufficiently strong to hold a threaded fastener when subjected to the relatively high tension forces found at various points of attachment. This problem will occur at any joint in which tension is exerted between the fastener's threads and sheet metal. Since the sheet metal is purposefully made as thin as possible, tension forces due to wind lift and the like can cause the threaded fastener to tear loose from the panel. It will be appreciated that a heretofore advantage of using pop rivets at such tension joints rather than threaded fasteners is that a relatively large bearing surface is achieved at the interface of the pop rivet and the inner surface of the metal sheet.
Thus, an important object of the present invention is to provide a means for securing a threaded fastener at a tension joint formed in a metal-foam-metal type prefabricated panel with mechanical performance equal or superior to a pop rivet or the like, yet without sacrificing economy and enabling disassembly with relative ease.